Circuit-switched voice connections over various telephone networks have been commonplace for over 100 years. With modern technology, people communicating over a voice connection can speak and listen to one another simultaneously because the communications connection is open in both directions continuously. As one party stops speaking, the other can continue at any point of time because the circuit-switched connection remains active all the time. The connection is terminated only when the parties so decide.
Communications connections, including voice connections, are increasingly packet-switched connections, like Internet connections, instead of being circuit-switched ones. One such packet-switched service/network is the GPRS (General Packet Radio Service) intended primarily for data communications. In a GPRS network, a communications connection is established only when there is data to transmit. An individual communications connection operates only in one direction at a time, either downlink towards the terminal, or uplink towards the backbone network. When no more data need to be transmitted or when there are momentarily no more packets to send, the link is disconnected. The packet-switched network can delay the removal of the link for a little time, typically for a: few hundred milliseconds. This is wise if packet transmission of newly arrived packets is to be continued or if a communications link in the other direction is to be established immediately after transmission in the previous direction ceases. The transmission of newly arrived packets or establishment of a new communications link in the other direction is quicker if the dedicated channel reserved for the previous communications link is still available, as opposed to that a new communications link has to be established from scratch through a common control channel in the network. In data transfer applications, the establishment of a new communications link in the other direction usually succeeds without problems because a computer can make a quick decision about a new communications link. If human reaction/action is required for the establishment of a new communications link, the arrangement usually will not work, because the time reserved for the decision-making is not long enough and the previous dedicated connection will be terminated.
One possible way of handling a voice connection between two or more persons over a packet-switched network is PoC (Push to talk over Cellular) the procedures of which are under development and standardization at present. The participants in a PoC session can receive non-voice data. Speech is interactive: speakers take turns randomly in a conversation, we can talk of discrete talk spurts. As one person stops talking and another one starts in his turn, there is a reaction time involved in this changeover, which may result in a situation where the dedicated channel reserved for the previous talk spurt is already released before the talk spurt of the other speaker starts. The release of the previous dedicated channel takes a few hundred milliseconds. After that, the dedicated channel needed must be established through a slower procedure by first employing the common control channel of the cellular network. This takes several hundred milliseconds. A similar problem occurs in conjunction with continuation of speech after a talk spurt. If the speaker wants to continue speaking and the link to the network has already been released, a new link must be established using the common control channel. If the release of the link is delayed, continuation of speech can occur more smoothly by just inserting new packets in the transmit buffer.
FIG. 1a shows an example case in which a terminal is receiving voice packets 1a, 2a and 3a. The voice packets end at packet 3a. After that, in a few hundred milliseconds, 4a, the dedicated channel is released. If the user of this terminal starts to speak only after that, which is probable, considering human reaction time, a new dedicated channel has to be set up for the terminal. The delay in setting up this new dedicated channel in accordance with the prior art is perceived by the users of terminals as an undesirable delay.